Thoracic CT andtransbronchial biopsy led to the diagnosis of a small-cell lung cancer.Extensive screening for autoantibodies was negative for intracellularantibodies (Hu, Ri, Yo, PCA-2, Tr, ANNA-3, AGNA-1, amphiphysin, CRMP-5, andGAD) and surface antibodies (NMDAR, AMPAR, GABA(A)R, GABA(B)R, mGluR1,mGluR5, LGI1, Caspr2, DPPX, neurexin-3α, and IgLON5). Here, GRM1 is linked to small cell lung carcinoma.